Plastic storage bags having zipper-type closures are known in the art and generally provide adequate closing function but do not provide especially good sealing. The rigid material used in the extrusion of the closures and the limitations on extruding tight tolerances in small plastic cross sections are not conducive to forming a hermetic seal.
U.S. Pat. No. 5,351,369 discloses a soft, compressible material extruded along the hooks and grooves of a closure to form a gasket. However, there is a limit on how much a material can reasonably compress. If there is too much material, then the closure won't close. If there is not enough material, the hermetic seal is not achieved. There is therefore very little tolerance for manufacturing variations. This presents challenges in that dimensions vary in production, which may prevent proper closure and sealing for a closure that requires such a precise fit. Gasket type closures are also seen in U.S. Pat. Nos. 4,892,414 and 8,196,269, in which a gasket film is pinched within closure profiles.
U.S. Pat. No. 5,689,866 discloses a hermetic seal created from a pressing rib that is fitted in between two hooks. This design has limitations in that when trying to fit the pressing rib in between the two hooks, there would be resistance forcing the pressing rib out. If the components are not strictly dimensionally controlled, the seal may not form correctly or the closure may not close due to the resistance force.
U.S. Pat. No. 6,854,886 discloses a watertight closure formed by having two collapsible members that press against each other when closed. In one embodiment, the collapsible member is made of a different material and the opposing member is not collapsible. This design has significant dimensional and compressibility limitations. There is only so much a material can reasonably compress. If there is too much material, the closure will not close. If there is not enough material, the seal may be inadequate.